An Injection well is a device that places fluid deep underground into porous rock formations, such as sandstone or limestone, or into or below the shallow soil layer. These fluids may be water, wastewater, brine (salt water), or water mixed with chemicals.
The UIC Program defines an injection well as:
A bored, drilled, or driven shaft, or a dug hole that is deeper than it is wide,
An improved sinkhole, or
A subsurface fluid distribution system.
How an injection well looks (is constructed) depends on the fluid injected and the depth of the injection zone. For example, deep wells that inject hazardous wastes or carbon dioxide (CO2) into isolated formations far below the Earth's surface are designed to provide multiple layers of protective casing and cement. Shallow wells that inject into or above drinking water sources are usually of simple construction and inject non-hazardous fluids.
What are injection wells used for?
Injection wells have a range of uses that include long term (CO2) storage, waste disposal, enhancing oil production, mining, and preventing salt water intrusion. Widespread use of injection wells began in the 1930s to dispose of brine generated during oil production. Injection effectively disposed of unwanted brine, preserved surface waters, and in some formations, enhanced the recovery of oil. In the 1950s, chemical companies began injecting industrial wastes into deep wells. As chemical manufacturing increased, so did the use of deep injection. Injection was a safe and inexpensive option for the disposal of unwanted and often hazardous industrial byproducts. In 2010, the EPA finalized regulations for geologic sequestration of CO2. This final rule created a new class of wells, Class VI. Class VI wells are used solely for the purpose of long term storage of CO2
How does the UIC Program categorize the different types of injection?
EPA’s regulations group injection wells into six groups or “classes.” Classes I - IV and VI include wells with similar functions, construction, and operating features. This allows consistent technical requirements to be applied to each well class. Class V wells are those that do not meet the description of any other well class. Wells in Class V do not necessarily have similar function, construction, or operating features.
Why does EPA regulate injection wells?
In 1974, Congress passed the Safe Drinking Water Act (SDWA). Part of SDWA required EPA to report back to Congress on waste disposal practices, and develop minimum federal requirements for injection practices that protect public health by preventing injection wells from contaminating underground sources of drinking water (USDWs).
What is a USDW?
An underground source of drinking water (USDW) is an aquifer or a part of an aquifer that is currently used as a drinking water source or may be needed as a drinking water source in the future. Specifically, a USDW:
Supplies any public water system, or
Contains a sufficient quantity of ground water to supply a public water system, and
currently supplies drinking water for human consumption, or
contains fewer than 10,000 mg/l total dissolved solids (TDS), and
Is not an exempted aquifer
The UIC Program implements this protective mandate through the UIC regulations.
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